The present invention relates to disc drive storage systems. More particularly, the present invention relates to spin valve sensors for use in disc drive storage systems.
Disc drives are the primary devices employed for mass storage of computer programs and data used in computer systems. Disc drives typically use rigid discs, which are coated with a magnetizable medium for storage of digital information in a plurality of circular, concentric data tracks. A read/write head is adapted to read information from and write information to the data tracks.
The head is carried by a slider which is connected to an actuator mechanism through a gimbaled attachment. The actuator mechanism moves the slider from track-to-track across the surface of the disc under control of electronic circuitry. The actuator mechanism includes a suspension assembly that applies a load force to the slider to urge the slider toward the disc. As the disc rotates, air is dragged and compressed under bearing surfaces of the slider that create a hydrodynamic lifting force which counteracts the load force and causes the slider to lift and xe2x80x9cflyxe2x80x9d in close proximity to the disc surface. The gimbaled attachment between the slider and the suspension assembly allows the slider to pitch and roll as it follows the typography of the disc.
Giant magnetoresistive (GMR) sensors are used as read elements in read/write heads to read data recorded on the magnetic discs of the disc drive. The data are recorded as magnetic domains in the recording medium. As the data moves past an active region of the read element, the data causes changes in magnetic flux to the GMR sensor, which causes changes in the electrical impedance of the GMR sensor. A signal representing these impedance changes and, thus, the recorded data, is obtained by applying a bias or sense current through the sensor. Decoding circuitry is used to analyze the signal and retrieve the data. Typical read sensors utilizing the GMR effect, frequently referred to as xe2x80x9cspin valvexe2x80x9d sensors, are known in the art. These spin valve sensors are multi-layered structures consisting of two ferromagnetic (FM) layers separated by a thin non-ferromagnetic layer. One of the ferromagnetic layers is called the xe2x80x9cpinned layerxe2x80x9d because its magnetization is magnetically pinned or oriented in a fixed and unchanging direction by an adjacent anti-ferromagnetic (AFM) layer, commonly referred to as the xe2x80x9cpinning layer,xe2x80x9d through an anti-ferromagnetic exchange coupling. The other ferromagnetic layer is called the xe2x80x9cfreexe2x80x9d or xe2x80x9cunpinnedxe2x80x9d layer because its magnetization is allowed to rotate in response to the presence of external magnetic fields. The impedance of the spin valve varies as a function of the angle between the magnetization of the free layer and the magnetization of the pinned layer thereby producing the GMR effect. Contact layers are attached to the spin valve sensor to apply the sense current and obtain the signal from which the recorded data is obtained.
There is a never-ending demand for higher data storage capacity in disc drives. One measure of the data storage capacity is the areal density of the bits at which the disc drive is capable of reading and writing. The areal density is generally defined as the number of bits per unit length along a track (linear density and units of bits per inch) multiplied by the number of tracks available per unit length in the radial direction of the disc (track density in units of track per inch or TPI). Currently, there is a need for areal densities on the order of 100 Gb/in2 which requires a track density on the order of 100-150 kTPI and greater.
One way to increase areal density of the data stored on a disc is to increase the track density by decreasing the track width and spacing between tracks. The smaller track widths and spacing require read elements with decreased active region widths and increased sensitivity to changing magnetic fields within the active region while avoiding side-reading. Side-reading occurs when a magnetic head responds to changing magnetic fields produced by adjacent tracks. This side-reading is a source of noise in the recovered data signal, and a source of cross-talk, a phenomenon where the read element reads data from two or more adjacent tracks. Consequently, the effects of side-reading in a read head is a limiting factor on the spacing between adjacent tracks, and hence a limiting factor to increased areal density.
The prior art teaches that in order for a GMR element to operate optimally, a longitudinal bias field should be applied to the free layer. The longitudinal bias field extends parallel to the surface of the recording media and parallel to the lengthwise direction of the GMR element. The function of the longitudinal bias field is to suppress Barkhausen noise which originates from multi-domain activities in the free layer of the GMR element. However, while it is important that the longitudinal bias field be strong enough to suppress the multi-domain activities in the free layer, it is also important for high areal density recordings that the longitudinal bias field be weak enough to allow the magnetization of the free layer to remain sensitive to external magnetic fields in the active region of the sensor.
Currently, two main longitudinal bias schemes for stabilization of the free layer are widely used. One scheme is based on the formation of a continuous free layer with end regions, which are longitudinally biased through an exchange coupling with adjoining anti-ferromagnetic patterns. The active region of the free layer is maintained in the desired single domain state due to the longitudinal bias field generated at the end regions of the free layer. In this scheme, the width of the active region of the free layer is primarily defined by the spacing of the conductor leads. Examples of such longitudinal bias schemes are described in U.S. Pat. Nos. 4,663,685 and 5,206,590. Although spin valve sensors with this type of longitudinal bias scheme exhibit satisfactory magnetic stability and sensitivity, they have relatively low track resolution due to side-reading at overlaid and regions of the free layer.
Another longitudinal biasing scheme is provided using permanent magnets which form abutted junctions to ends of the spin valve stack. In this scheme, the active region of the spin valve sensor is defined by the spacing between the abutted junctions. An example of a spin valve sensor using this longitudinal biasing scheme is described in U.S. Pat. No. 5,742,162 and is generally illustrated in FIG. 1. The spin valve sensor 300 includes a sensor stack 302 that includes a ferromagnetic free layer 304 formed on an insulating layer 305, and AFM layer 306 that pins a magnetization of ferromagnetic pinned layer 308, and a conducting layer 310. Permanent magnets 312 form abutted junctions to ends of the sensor stack and longitudinally bias the magnetization 314 in free layer 304. A sense current 316 is delivered through the conducting layer 310 from conductor leads 318 which form abutted junctions to the ends of the spin valve stack 302. The width of the active region of the spin valve sensor 300 is generally defined by the spacing between the permanent magnets 312 and the conductor leads 318. The longitudinal bias field produced by the permanent magnets 312 is strong over the width of the active region resulting in enhanced track resolution but low sensitivity to external magnetic fields applied to the active region of the sensor.
It is known that the sensitivity of spin valve sensors having permanent magnets that form abutted junctions with the sensor stack can be enhanced by utilizing conductor leads that overlay the sensor stack as shown in the spin valve sensor 320 of FIG. 2. Spin valve sensor 320 generally includes the same elements of sensor 300 of FIG. 1, but with the modification of permanent magnets 312 forming an abutted junction with the entire sensor stack 302 while conductor leads 318 overlay end regions of the sensor stack. For a given active region width, the spin valve sensor 320 with overlay conductor leads 318 has better sensitivity than spin valve sensor 300 with conductor leads 318 forming abutted junctions with the sensor stack 302, due to greater spacing between permanent magnets 312 and the center of the ferromagnetic free layer 304. The larger separation results in a reduction of the magnitude of the longitudinal bias field generated by permanent magnets 312 in the center of ferromagnetic free layer 304 and increases the permeability of ferromagnetic free layer 304 in the central active region of sensor 320, on which the sensitivity of the sensor depends. However, spin valve sensors with these spaced permanent magnet abutting junctions and overlay conductor leads have lower track resolution than sensors having permanent magnets and conductor leads forming abutted junctions with the sensor stack, due to the much higher permeability of the portions of the free layer which are overlaid by the conductor leads. This results in undesirable oscillations of the magnetization in the overlaid regions of the free layer. Additionally, the conductor leads have a resistivity, which causes the sense current 316 to flow through the spin valve stack 302 under the overlaid portions resulting in increased side-reading problems.
There exists a continuing demand for increased areal densities in magnetic data storage systems. To accommodate this demand, advancements in GMR sensor designs are required in the areas of reducing side-reading while improving sensitivity to applied magnetic fields.
The present invention is directed to a spin valve sensor for use with a data storage system having high sensitivity while avoiding problems with side-reading and cross-talk. The spin valve sensor includes free and pinned ferromagnetic (FM) layers, a conducting layer therebetween, contact leads, free layer biasing elements, and an anti-ferromagnetic (AFM) layer. The pinned layer has opposing ends, which define a width of an active region of the spin valve sensor having a giant magnetoresistive effect in response to applied magnetic fields. The free layer is positioned below the pinned layer and has opposing ends that extend beyond the active region. The contact leads abut the pinned layer and overlay portions of the conducting layer. The free layer biasing elements abut the ends of the free layer and bias the magnetization of the free layer in a longitudinal direction.
These and other features and benefits would become apparent with a careful review of the following drawings and the corresponding detailed description.